IronRuby is an open-source implementation of the Ruby
programming language which is tightly integrated with the
.NET Framework. IronRuby can use the .NET Framework and
Ruby libraries, and other .NET languages can use
Ruby code just as easily.

Why IronRuby?

IronRuby is an excellent addition to the .NET Framework, providing Ruby
developers with the power of the .NET framework. Existing .NET developers can
also use IronRuby as a fast and expressive scripting language for embedding,
testing, or writing a new application from scratch.

The CLR is a great platform for creating programming languages, and the DLR
makes it all the better for dynamic languages. Also, the .NET framework
(base class library, presentation foundation, Silverlight, etc.) gives
developers an amazing amount of functionality and power.